FIG. 1 shows a conventional architecture of an optical network. The network architecture is hierarchical having the highest data rates in an optical core network, such as a back-bone network of a country. To each core network several optical metro networks can be connected, for instance in a ring structure. To each metro network in turn several access networks can be connected. The edge of the network as shown in FIG. 1 is formed by terminal devices T which can be connected via xDSL (version of Digital Subscriber Line) to a host device, for example to a switch in an DSLAM (Digital Subscriber Line Access Multiplexer). This switch is connected via an optical transport system (designated as FSP in all figures) and optical transport means to a transport system of a local exchange. The core, metro and access network can have a ring structure, for example formed by two optical fibres and by transport systems. The optical fibres can transport data by means of wave length division multiplexing WDM. In wave length division multiplexing WDM optical carrier signals are multiplexed on a single optical fibre by using different wave lengths λ (colours) to carry different data signals. This allows an increased bandwidth and makes it possible to perform bidirectional communication over one strand of fibre. WDM-systems allow to expand the capacity of a network without laying more fibre. The capacity of an optical fibre can be expanded by upgrading multiplexers and demultiplexers at each end. This is often done by using optical-to-electrical-to-optical conversion at the edge of the transport network to permit interoperation with existing equipment. WDM-systems can be divided in different wave length patterns, i.e. conventional or coarse and dense WDM (CWDM, DWDM). A recent development relating course WDM is the creation of GBIC (Gigabit Interface Converter) and Small Form Factor Pluggable (SFP) transceivers using standardized CWDM-wave lengths.
As can be seen from FIG. 1, an optical network can be formed by two main components, i.e. by a transport system and by host devices. Host devices include switching devices, such as routers, bridges, Ethernet switches, fibre channel switches or cross-connects. The network architecture as shown in FIG. 1 comprises optical interconnections, optical transport systems and host devices, such as switches or routers. The separation of functionality in two different device types of the conventional network as shown in FIG. 1, i.e. on the one hand transport of data (by the transport system) and on the other hand aggregation/switching data (by the host devices) increases complexity and costs.
Accordingly, it has been proposed to shift functionality of the transport system, in particular the electrical-to-optical conversion, into the host device by using pluggable transceivers.
A small form factor pluggable (SFP) is a compact optical transceiver using optical communication. A conventional small form factor pluggable module interfaces a network device mother board of a host device, such as a switch or router to an optical fibre or unshielded twisted pair networking cable. The SFP-transceivers are available in a variety of different transmitter and receiver types allowing users to select an appropriate transceiver for each link to provide a required optical reach over the available optical fibre type.
A SFP-transceiver is specified by a multi-source agreement (MSA) between competing manufacturers. The SFP-module is designed after the GBIC-interface and allows greater data port density (i.e. number of transceivers per inch along the edge of a mother board) than GBIC. SFP-transceivers are commercially available and have a capability for data rates up to 4.25 Gbit/sec. A variant standard, XFP, is capable of 10 Gbit/sec.
Some SFP-transceivers support digital optical monitoring functions according to the industry standards SSF 8472 (ftp://ftp.seagate.com/sff/SFF-8472.PDF) multi-source agreement (MSA). This makes it possible for an end user to monitor real time parameters of the SFP-module, such as optical output power, optical input power, temperature, laser bias current and transceiver supply voltage.
FIGS. 2, 3 show a conventional pluggable standard SFP-transceiver module. The SFP pluggable module comprises an electrical interface connecting the pluggable module with a mother board of a host device by plugging the module into a cage of the host device board. On the front side of the pluggable module at least one optical fibre is attached to the module.
FIG. 4 shows a conventional system with pluggable SFP-transceivers. A host device, such as a switch or router, comprises a controller which is connected via a backplane to interface cards each having several cages which allow to plug in SFP-modules as shown in FIG. 3. A transceiver within the pluggable module performs a conversion of the applied electrical signals to an optical signal which is forwarded via an optical fibre to the transport system. The transport system comprises several cards which comprise several cages for plug-in SFP-transceiver modules. These interface cards allow a switching, i.e. multiplexing or demultiplexing of signals within the electrical domain in response to control signals generated by a controller of the transport system and received via an internal management connection. From the interface cards within the transport system the switched or controlled signals are applied to further modules for optical signals or optical fibres. These modules can, for example comprise variable optical attenuators (VOA), multiplexers/demultiplexers, amplifiers, switchers etc. From the transport system connected to the near end host device, the signals are forwarded via optical fibres to remote far end transport systems over a distance of many kilometers, wherein the remote transport systems are in turn connected to far end host devices.
The conventional system as shown in FIG. 4 as a the disadvantage that the complexity of the system is quite high because three domain conversions on the near end side and on the far end side have to be performed. As can be seen from FIG. 4, an electrical signal of the near end host device is converted within the pluggable SFP-transceivers plugged into the interface card of the host device to an optical signal and then retransformed from the optical domain to the electrical domain by a SFP-transceiver plugged into a cage of an interface card of the transport system. After an electrical switching is performed depending on the control signal supplied by the controller of the transport system, the electrical signal is again transformed from the electrical domain into an optical domain by another plugged in SFP-transceiver. Accordingly at the near end side, three domain conversions, i.e. an electrical-to-optical, an optical-to-electrical and an electrical-to-optical conversion are necessary. On the far end side, the three conversions are performed again resulting in a total of six domain conversions. Because of the necessary domain conversions, the technical complexity of the system is quite high. Since two different devices, i.e. a host device and a transport system have to be provided on each side management efforts, the occupied space and power consumption are increased.
Conventional MSA compatible transceivers provide only data transmission functions. Accordingly, conventional transceivers and MSA compatible transceivers which are provided within a pluggable module operate only on an optical layer. All other functions, such as management and data traffic analysis for data protocol analysis are either performed by the host devices or external separate devices.
To provide protocol based services by a network operator a bidirectional transmission of data to the client is necessary. Furthermore, monitoring of the performance of the respective service is necessary, since the transmission characteristics of the data transmission channel can be compromised and can affect the performance of the respective service negatively.
In a conventional network or system a monitoring of the service performance is done by means of active data transmission techniques at the location of the client during the measurement and evaluation of performance data, such as “loss of Ethernet frame”. An additional data transmission channel is provided for transmitting the measured performance data at the location of the client to the location of the network operator. With this kind of active performance monitoring it can be checked whether the system complies with SLAs and a detailed error analysis can be performed in case of failures.
However, the active transmission technique as used in a conventional system to monitor the performance of a provided service has several disadvantages. A separate apparatus has to be provided and carried to the location of the client. Hence, there is a statistic probability that the active data transmission technique fails and the operational availability of the network is reduced. Furthermore, performance monitoring by means of an active data transmission technique at the side of the client is laborious and takes considerable efforts.
Accordingly, it is an object of the present invention to provide a method and a system to overcome the above mentioned problems and which provide a reliable and easy to handle monitoring of a service performance.